Speed is King

Speed is King

Adam Kall, Director of Science

5 minute read

The operating environment of space requires speeds and forces that boggle the mind, but before we discuss speed in space we have to look at the steps taken to reach such achievements.

Horses were first domesticated 6,000 years ago, and up until 1830 their galloping speed of 30 mph was the fastest humans could move between two locations. When the steam engine was invented, and later placed in a locomotive, speeds started to increase to as high as 78 mph. Critics feared such speeds would suck the air away, rendering passengers unable to breathe. Once they realized a strong wind won’t leave a vacuum behind it, the race was on to continue accelerating how fast people and things can be moved. By 1904, the new toy that was the internal combustion engine was pushing barriers in cars, specifically the 100 mph barrier. Internal combustion was also the key to powered flight in 1903, and thanks to flying vehicles not having to overcome friction with the ground, they would soon overtake other inventions for the title of fastest at speeds never thought possible.

Due to the advantages of going faster than the enemy, World War II pushed airplane design to its limits. In 1944, secret German planes were using rocket engines and reached a speed of 702 mph, but pilots were reporting strange behavior. As they approached the speed of sound at 767 mph it became harder to accelerate and use their controls. After the war, the American pilot Chuck Yeager succeeded in passing the sound barrier and became the first human to travel supersonic at a speed of 891 mph. Since then the aerospace industry continued to increase speed by flying higher, where there is less air and therefore less friction, culminating in the current air-speed record, set by Captain Eldon W. Joersz and Major George T. Morgan Jr. in an SR-71 Blackbird, of 2,193.2 mph. However, this record was set in 1976, but 7 years prior the record for fastest moving humans had already been reached by the Apollo astronauts, and they were faster by an order of magnitude. Yet for these astronauts, being the fastest humans in history was never a part of their mission. In the environment of space, travelling more than 28 times the speed of sound isn’t a challenge, but a regular occurrence of the environment.

Humans struggled to go faster and faster, but once a high enough speed is achieved, the result becomes an orbit around the planet - a strange circumstance where an object can stay in the sky indefinitely by moving over the ground fast enough to chase the horizon. At these speeds much of physics gets wibbly-wobbly. When discussing spacecraft and orbital behavior, it is easy to forget about the speeds involved in the environment of space and not realize what this speed means for most interactions. Much like watching a plane flying high in the sky, it is easy to get the impression that a spacecraft is moving quickly, but that it is not the fastest moving physical object a person will see in their lifetime. This misconception is further supported by every video of two spacecraft operating in close proximity showing a slow dance, more akin to ships in a harbor (not usually what comes to mind when imagining the term “speed”). The reason for all of this is that spacecraft have to move incredibly fast, relative to the Earth, in order to stay in orbit. The hypothetical speedometer of the International Space Station is up at over 17,000 mph (the speed of sound is only 767 mph) or 7.66 kilometers per second. For those who don’t use kilometers often in their daily lives, a spacecraft would complete a 5K run in 0.65 seconds, which happens to be nearly 12 minutes and 35 seconds faster than the world record of 12 minutes and 35 seconds.

These speeds are only possible because high above the Earth there is nothing for the spacecraft to run into, thus any force used to push it just adds to its speed without fighting against some opposite force. If something happens to be in the way of an orbiting spacecraft, say another satellite or a piece of space debris moving at orbital speed in a different direction, then the collision has some frightening effects. The simplest equation used to explain the impact is the Kinetic Energy equation, or one half of the mass times velocity squared, which gives how many joules of energy are imparted in the collision. A metric ton of TNT contains 4.2 Gigajoules, so at relative speeds of 12 kilometers per second, a small satellite the size of a washing machine in orbit would impart the energy of 1.2 tons of TNT. An explosion of that magnitude on Earth would have a large fireball and shockwave, but in space these effects don’t happen (I’ve detailed what does happen and why in a previous column, found here). We could imagine a situation where the washing machine strikes a much smaller object, say a wrench weighing only 100 grams, dropped by an astronaut on a space walk long ago. If the washing machine and wrench all stay in one piece (they won’t but let’s pretend that they would), and no energy was lost in the collision to heat, then the wrench would be punted off at 18 kilometers per second. Considering that the speed necessary to escape the solar system is 16.6 kilometers per second, the wrench will have joined the ranks of objects like the Voyager spacecraft as it soars off to another solar system.

If only reality was so kind as to have collision with space debris result in the space debris leaving the solar system. Instead, the energies at those speeds interact in such a way as to transform the washing machine-sized satellite into thousands of small bits of new space debris, each travelling at orbital speeds, or faster, in new directions. As seen from the wrench versus washing machine matchup, the energy of even a small object impacting a larger object is catastrophic at orbital speed. Thus speed is king, because speed is always the determining factor.

As these risks do not change without intervention, active effort must be taken to safely and securely retrieve these hypersonic hazards, that is those floating wrenches and bits of washing machine. This is the problem that KMI aims to solve, by removing the debris in orbit before it collides. Keep up to date with us in our mission to keep space clear for all.